Resistance material for fire detector element



United States No Drawing. Application October 26, 1954 Serial No. 464,907

2 Claims. (Cl. 252-518) The present invention relates to fire detector elements, and, more particularly, to a core composed of a resistance material adapted to be utilized in connection with such elements.

The invention is concerned with fire detector elements comprising two or more spaced apart conductors of electricity having'therebetween a core composition of such a resistance at normal temperatures that, in efiect, it insulates the conductors, and of such a resistance at a predetermined higher temperature that it becomes a conductor of electricity between the conductors and enables suflicient current to pass through the conductors to operate a device for controlling a fire alarm and/ or fire extinguishing circuit. For example, as shown in United States Letters Patent No. 2,586,252, the elements may be in the form of a cable-like structure adapted to be placed in a space where a fire is to be detected. This structure comprises a metallic tube through which electrically conductive wires extend which are separated from each other and the tube by a suitable resistance material of the foregoing character.

More specifically, the present invention is primarily concerned with improving this resistance material in a manner to more accurately predetermine the temperature at which it is rendered conductive in response to the heat of a fire, whereby current can flow through the conductors to operate an electrical device.

Accordingly, an object of the present invention is to provide an improved resistance material of the character indicated herein.

Another object is to provide such a material which becomes electrically conductive practically instantaneously when heated to a relatively low, predetermined temperature.

A further object is to provide such a material which is economical to prepare, is reliable in operation, and is fully adapted for repeated use without change in its responsive characteristic.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will :be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

In accordance with the present invention, it has been [found that the foregoing objects can be accomplished 'by utilizing a resistance material, comprising'manganese dioxide, zirconium silicate, a frit and an inert ceramic body.

The manganese dioxide and zirconium silicate may be of a chemically pure or technical grade. I

The frit may be any of the well known frits described in the literature which are generally utilized in providing the so called enamel base coating on metallic kitchenware and the like. This frit when used in a suflicient amount, serves as a body or carrier for the manganese 2,871,197 Patented Jan. 27, 1 959 chemical composition does not materially afiect thelelectrical properties 'of the composition about tobe described. Byway of example such a frit may :be prepared-by melting, solidifying and grinding'a mixture comprising Twenty five parts by weight of this frit are then combined with seventy five parts by weight of a mixture consisting of 90% steatite and 10% flour.

The manganese dioxide, zirconium silicate, frit, steatite and flour are dry blended, and suflicient water is added to make the mixture plastic. The plastic mass is then extruded onto the wires and is baked at about 2,000 F. to fuse the same to the wires as the water is driven olf and the flour is burnt out.

It has been discovered that the amount of manganese dioxide in the composition determines the temperature at which the-core becomes conductive. For example, a mixture of about 50% manganese dioxide, about 12.5% frit, about 33.75% steatite and about 3.75% flour, to which about 4 parts by weight of zirconium silicate have been added, produces cores which become conductive at a temperature of about 300 F.

It has further been discovered that the zirconium silicate acts as a fiuxing agent to provide for good adherence of the core composition to the wires, gives the core composition a high structural strength, particularly high green strength, and gives the core composition a high initial resistance which drops sharply at the predetermined temperature to render the composition conductive.

The following formula illustrates a specific core composition in accordance with the present invention.

Parts by weight Manganese dioxide 50 Frit 12.5 Steatite 33.75 Flour 3.75 Zirconium silicate 4 A composition was produced from these materials and was applied to two-wire temperature sensing elements in the foregoing described manner. The wires were composed of Inconel, and had a length of ten feet and a diameter of .010 inch. This core had a diameter of .058 inch, and the wires were disposed therein in parallel relation about .010 inch apart throughout their length. These sensing elements had an infinite resistance at F. which dropped sharply to about 5,000 ohms when the composition was heated to 300 F. thereby enabling sufficient direct current or alternating current to flow through the wires to effect operation of an electrical device for giving an indication that the aforementioned temperature condition existed.

From the foregoing description, it will be seen that the present invention provides a composition for temand reliable indication that such temperature has been dioxide to place the composition in glass phase, but its detected.

It will be understood that the details and examples hereinbefore set forth are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

3 We claim:

1. A resistance material consisting essentially of about 50 parts by weight of manganese dioxide, about 4 parts by weight of zirconium silicate, about 12.5 parts by weight of a frit, and about 33.75 parts by weight of steatite;

2. A resistance material extrudable'as a plastic 'mass onto electrical conductors and adapted to be fused thereon, said material consisting essentially'of about 50 parts by weight of manganese dioxide, about 4 parts by weight of zirconium silicate, about 12.5 parts by weight of a frit, about 33.75 parts by weight of steatite, about 3.75

parts by weight of flour and suficient water to render the material extrudable.

References Cited in the file of this patent UNITED STATES PATENTS Peters ,Jan. 31, 1950 Squier Mar. 4, 1952 OTHER REFERENCES ceramie Industry,;]'an. 195 4, pag e133. 

1. A RESISTANCE MATERIAL EXTRUDABLE AS A PLASTIC MASS ONTO ELECTRICAL CONDUCTORS AND ADAPTED TO BE FUSED THERON, SAID MATERIAL CONSISTING ESSENTIALLY OF ABOUT 50 PARTS BY WEGHT OF MANGANESE DIOXIDE, ABOUT 4 PARTS BY WEIGHT OF ZIRCONIUM SILICATE, ABOUT 12.5 PARTS BY WEIGHT OF A FRIT, ABOUT 33.75 PARTS BY WEIGHT OF STEATIE, ABOUT 3.75 PARTS BY WEIGHT OF FLOUR AND SUFFIEIENT WATER TO RENDER THE MATERIAL EXTRUDABLE. 